In dialysis procedurers, blood is taken out of the body in an extra-corporeal closed circuit and passes on one side of a membrane located in a dialyser. A dialysis solution circulates on the other side of the membrane. A dialysis machine contains the necessary pumps and other equipment for performing and monitoring the dialysis process, which can be hemodialysis, hemodiafiltration and/or hemo-filtration.
In order to ensure that no dangerous conditions arise for the patient, the dialysis machine is provided with several pressure transducers, which can be arranged at different positions along the extra-corporeal blood circuit. Examples of the use of pressure transducers in such systems are disclosed European Patent Nos. 130,441 and 134,436, which show cassettes with integrated connections to such pressure transducers positioned in the dialysis machine.
Apart from the pressure transducers which are disclosed in these patents, the pressure transducers themselves are intended for connection to tubes. Luer-couplings of the male type are thus mounted on the front of the dialysis machine. Each luer-coupling is connected to a pressure transducer inside the machine by means of a tube, and the pressure transducer converts the pressure in the tube into an electric signal. This pressure transducer is normally mounted on a circuit board. The pressure at the orifice of the luer-coupling is transmitted through the tube to the pressure transducer, with air in the tube acting as the pressure medium. The tube between the luer-coupling and the pressure transducer is provided with a filter, the function of which is to prevent fluid, particularly blood, being able to reach the pressure transducer. Thus, the filter only allows air to pass therethrough.
The apparatus, of which the pressure is to be sensed, is connected to the luer-coupling. An example of such an apparatus is a drip chamber or air separator positioned on the venus side of a tube-set. A tube leeads from the upper end of the drip chamber, and the tube is provided with a blood filter and a luer-coupling of the female type. This luer-coupling of the female type can be connected with the luer-coupling of the male type which is positioned on the front of the dialysis machine so that the machine can monitor the venous pressure in the drip chamber.
By arranging a blood filter in the tube from the drip chamber it is ensured that blood is not able to reach the luer-coupling positioned on the front of the dialysis machine. As a means of double safety the aforementioned blood filter is positioned in the tube between the luer-coupling and the pressure transducer within the machine.
When servicing dialysis machines of the type designated as in GAMBRO AK 100 we have found that it is inevitable that in some cases blood passes to the male type luer-coupling and into the interior of the machine. In principal this should not be possible, since the outer blood filter should prevent such blood leakage.
Cleaning of a machine which has been subjected to such blood leakage is relatively complicated, and has to be carried out by specially trained service personnel. In this case the tube positioned in the machine is replaced and the luer-coupling in the machine is cleaned. If the luer-coupling cannot be cleaned this must be replaced as well.
Hopefully, the blood filter within the machine has remained intact and, if so, the pressure transducer can be retained. Otherwise, even this must be replaced, which is very expensive.
It is presumed that many of the discovered cases of blood leakage are caused by the fact that the dialysis machine is used with tube-sets of a basic type which lack separate blood filters. However, with the provision of double safety measures, the dialysis machine can, despite this, be saved from the necessity for costly repairs.
When handling blood in an extra-corporeal closed circuit, measures must be taken to minimize the risk of infection, particularly with hepatitis and AIDS. Blood which leaks into the machine and remains there can be a source of infection for the next patient, and, therefore, a machine where leakage has occurred must be attended to immediately.
The insert according to the present invention can also be used in connection with the sensing of pressure in circuits which contain fluids other than blood, such as in machines intended for other medical uses, for example in connection with infusion or peritoneal dialysis.